1. Field of the Invention
This invention relates to a tunnel kiln suitable for firing ceramic shaped bodies and the like.
2. Related Art Statement
Heretofore, a tunnel kiln comprising a preheating zone for preheating a shaped body to be fired, a firing zone for sintering the shaped body and a cooling zone for cooling a fired body has been used for firing a ceramic shaped body containing a shaping assistant such as an organic resin or the like.
FIG. 5 shows a sectional view of a preheating zone of a conventional kiln, wherein the firing of the shaped body is carried out by placing a shaped body 11 to be fired on a truck 12 and transferring it inside a furnace defined by furnace wall 13 so as to pass through the preheating zone, firing zone and cooling zone. In FIG. 5, an atmosphere gas heated by means of a combustion burner or the like (not shown) is discharged into the exterior of the kiln through an atmosphere gas outlet 14 arranged in the furnace wall 13 by means of a blower 15, while a sand seal 16 is arranged adjacent a lower portion of the furnace wall 13 to provided a seal between the atmosphere inside the furnace and the wheel of the truck.
In the preheating zone of the tunnel kiln of the above structure, however, the shaping assistant included in the shaped body is decomposed by heating in the preheating or firing of the shaped body to produce a decomposition product 17 of the shaping assistant (hereinafter referred to as a decomposition product).
This decomposition product 17 is initially in the form of a gas or mist but is cooled while approaching the atmosphere gas outlet 14 together with the atmosphere gas to form a liquid and further cooled to form a solid, if possible, which adheres to the inner wall of the furnace or the atmosphere gas outlet.
As the adhesion of the decomposition product 17 occurs, clogging of the atmosphere gas outlet 14 results, or the decomposition product 17 descending downward from the furnace wall 13 by its dead-weight flows into the sand seal 16 partitioning between the inside of the furnace and the wheel of the truck, whereby granular sands are bonded to each other through the decomposition product in the form of agglomerates or dumplings to lower the sand seal effect. Consequently it is feared that of exposing the wheel portion of the truck will be exposed to high temperatures or the like. Furthermore, these agglomerates or dumplings go from gaps between iron plates for sand seal into the vicinity of rails for the truck, and finally the derailment of the truck or the damage of the wheel may be caused.
Therefore, a great labor has been taken for removing the decomposition product 17 adhered to the furnace wall 13 and the atmosphere gas outlet 14.